Recently, high-speed cellular radio communication schemes such as Long Term Evolution (LTE) and WiMAX are being practically implemented, and the communication rate of radio communication services enjoyed by mobile users has greatly improved. Furthermore, if fourth-generation cellular radio communication schemes such as LTE-Advanced (LTE-A) are introduced, an even greater improvement in communication rate is anticipated.
On the other hand, the number of mobile users is increasing rapidly, and the usage of applications demanding high data rates is becoming more widespread. As a result, the development of cellular radio communication schemes is not fully satisfying all mobile users' needs. Consequently, in order to supplement macro cells and increase communication capacity, the introduction of small cells is being advanced. Small cells are a concept that encompasses femto cells, nano cells, pico cells, micro cells, and the like. Small cells are typically introduced by installing a base station (also called an access point) that is small compared to a macro cell base station (for example, an evolved Node B (eNB) in LTE). However, in areas where a macro cell and a small cell overlap, there is a risk of radio signals transmitted and received by the small cell interfering with a terminal connected to the macro cell.
In order to avoid the risk of interference due to the introduction of small cells, Patent Literature 1 below proposes a technique that cooperatively controls the transmit power and transmission rate of a macro cell and a small cell.